Terachai's place at 16/17 Soi Sukhumvit 19 was a short walk to and from Asok station/Terminal 21. You don't have to walk that far into the soi/lane. He gave great instructions and photos on how to get to his place. All I had to do was to show those photos when I was a bit unsure where it was. Excellent idea with the photos!
His on-site housekeeper was very helpful too. Although my room was on 3rd floor of the walk-up apartment, it was manageable as there were not a lot of steps to the next floor. All in all an excellent stay. Definitely recommend it to anyone. A tip from friends, the food court at Terminal 21 is about one of the cheapest ones along that stretch of Bangkok.